PSFB Deep dive

I. Introduction to PSFB Converters

Definition and Core Functionality

Phase-Shifted Full-Bridge (PSFB) converters represent a specialized class of isolated DC-DC converters. Their primary function involves stepping down high DC bus voltages to lower, regulated DC outputs. A fundamental and critical feature of this topology is the provision of galvanic isolation between the input and output stages, which is achieved through the integration of a high-frequency transformer.¹

The core operational principle of a PSFB converter revolves around a full-bridge inverter circuit positioned on the primary side of the isolation transformer. On the secondary side, a rectification stage, which can be either diode-based or utilize synchronous rectification (SR) with MOSFETs, converts the transformer’s AC output back to DC. The distinguishing characteristic that sets PSFB converters apart from conventional full-bridge topologies is their unique phase-shifting control mechanism. This mechanism is precisely engineered to regulate the amount of power transferred from the primary to the secondary side, thereby controlling the output voltage.¹

Historical Context and Role in Power Conversion

The PSFB topology has undergone significant evolution over several decades, particularly in its application for medium to high-power regulation. Historically, these converters operated at relatively low kilohertz switching frequencies. However, advancements in power electronics technology, including the development of new materials and devices, have enabled modern PSFB designs to operate efficiently at hundreds of kilohertz. This increase in switching frequency has dramatically reduced the physical size of converters, often by a factor of 5 to 10 or more, while simultaneously boosting their efficiency to levels frequently exceeding 95%.¹

As a derivative of the conventional hard-switched full-bridge converter, the PSFB topology was developed to address the inherent switching losses prevalent in its predecessors. It achieves this by incorporating soft-switching capabilities, most notably Zero Voltage Switching (ZVS). This innovation has been pivotal in positioning the PSFB converter as a cornerstone in the realm of high-performance power conversion, allowing for more compact, efficient, and reliable power supplies compared to traditional hard-switched designs.⁵

Key Characteristics and Applications Overview

PSFB converters are ideally suited for medium to high-power applications, typically handling power levels ranging from several hundred watts to over 10 kilowatts. They are particularly effective in scenarios involving high DC input bus voltages, often derived from a Power Factor Correction (PFC) stage, and are frequently employed when a regulated low output voltage with high current capability is required.²

Their widespread adoption is evident across a diverse array of sectors, highlighting their versatility and robust performance:

Telecommunications Systems: PSFB converters are extensively used in telecom rectifiers to convert high voltage DC buses (e.g., 400V) to intermediate distribution voltages (e.g., 48V). In these applications, galvanic isolation is a critical safety and performance requirement, ensuring protection from the line voltage.¹
Server Power Supplies: They serve as the front-end DC-DC converter stage in data centers, stepping down regulated DC bus voltages (e.g., 390V) to lower, tightly regulated outputs (e.g., 12V, 24V, 48V). High efficiency and reliability are paramount in this sector due to the massive power consumption of servers and the common use of redundant power supply structures.¹
Electric Vehicle (EV) Charging Systems: PSFB converters find broad utility in battery charging systems, encompassing both on-board and off-board EV chargers and dedicated EV charging stations. Their ability to handle a wide conversion range is particularly beneficial for charging various battery chemistries, such as Lithium-ion and Lead-acid, which demand precise voltage regulation across different charging phases.¹
Renewable Energy Systems: These converters are integrated into renewable energy infrastructures, including solar power generation systems and energy storage solutions. They facilitate efficient DC-DC conversion and provide isolation in these high-power applications, thereby enhancing the overall efficiency and reliability of grid-tied or off-grid renewable energy deployments.¹
Industrial Power Systems: PSFB converters are a general solution for high-power regulators and diverse industrial equipment. They are also employed in Auxiliary Power Units (APUs) within electric vehicles, where they convert high voltage battery pack power to lower voltages for internal loads like electric power steering and cooling pumps. Their high power density and soft-switching capabilities make them well-suited for demanding industrial environments.²

The extensive use of PSFB converters in demanding, high-power sectors such as telecommunications, servers, electric vehicles, and renewable energy systems indicates a significant preference for solutions offering high efficiency, robust isolation, and compact power delivery. This prevalence suggests that the inherent advantages of PSFB, particularly its soft-switching capabilities, effectively address the stringent requirements of these critical applications, often outweighing the complexities associated with their design. The consistent selection of PSFB for these applications underscores that its benefits, especially ZVS-enabled high efficiency and galvanic isolation, are highly valued and directly meet the core needs of these industries. This firmly establishes PSFB as a mature and preferred solution within its specific power niche.

II. Fundamental Topology and Operating Principles

Circuit Diagram and Key Components

The fundamental structure of a PSFB converter begins on the primary side, featuring a full-bridge configuration. This bridge is composed of four power electronic switches, typically MOSFETs or IGBTs, labeled QA, QB, QC, and QD. These switches are strategically connected to the primary winding of an isolation transformer, denoted as T1.¹ On the secondary side, the rectified output is achieved either through conventional diode rectifiers or, more commonly in high-performance designs, by employing MOSFET switches for synchronous rectification (SR). Following the rectification stage, an output filter, consisting of an inductor (Lo) and a capacitor (Co), smooths the rectified DC voltage to provide a stable output.¹

Crucially, the design accounts for inherent parasitic elements. Parasitic capacitances (Coss) are present across the MOSFET switches, and the transformer’s leakage inductance (Llkg) is not merely a parasitic to be minimized but a significant component utilized in the converter’s operation. In many designs, an additional resonant inductor (Lr), sometimes referred to as a “shim” inductor, is intentionally added in series with the primary winding. This external inductor augments the transformer’s leakage inductance, creating a resonant tank circuit essential for facilitating soft switching.¹

Detailed Phase-Shifting Control Mechanism

The control of a PSFB converter is distinct from traditional Pulse Width Modulation (PWM) techniques. Instead of varying the pulse width of individual switches to control the duty cycle, power regulation is achieved by adjusting the phase shift between the two legs of the full bridge. For instance, switches QA and QB form one leg, and they are switched complementarily (180 degrees out of phase) at a fixed 50% duty cycle, separated by a short dead time. Similarly, QC and QD form the second leg and operate with the same complementary 50% duty cycle.¹

The critical control parameter is the phase shift applied between the PWM switching signals of these two legs (e.g., the signals for leg QC-QD are phase-shifted with respect to those for leg QA-QB). This phase shift directly determines the amount of overlap between the diagonal switches (e.g., QA and QD, or QB and QC). The duration of this overlap, in turn, dictates the amount of energy transferred from the primary to the secondary side, thereby controlling the output voltage.¹

When diagonal switches are simultaneously ON, power is actively transferred to the load. However, a unique and fundamental aspect of the PSFB topology is the presence of a “freewheeling” or “recirculating” interval. During this interval, either the two upper switches (QA and QC) or the two lower switches (QB and QD) are turned ON simultaneously. This action effectively short-circuits the transformer primary winding, resulting in zero voltage being applied across it. Consequently, no power is transferred to the secondary during this period. The output power during this time is supplied by the energy stored in the output inductance. Critically, the primary current freewheels through this shorted path, maintaining its previous state and preventing it from decaying to zero. This short-circuiting action is fundamental to enabling Zero Voltage Switching (ZVS) for the primary switches.²

The fixed 50% duty cycle per leg, combined with the phase-shift modulation technique, represents a sophisticated control approach that inherently establishes the necessary conditions for soft switching. This design choice shifts the complexity from managing the individual duty cycles of each switch to precisely controlling the phase relationships and dead-times between the legs. This approach is particularly well-suited for implementation with modern digital controllers, which excel at precise timing and complex waveform generation. The intrinsic nature of this control scheme, by creating the freewheeling intervals, directly supports the soft-switching objectives of the PSFB converter, positioning it as an effective solution for high-frequency, high-power applications.

Operating Modes and Waveforms

The operation of a PSFB converter within a single switching cycle can be segmented into distinct modes, each characterized by specific switch states, the voltage applied across the transformer primary (V_PRI), and the behavior of both primary and secondary currents. While a full visual representation is often required for comprehensive understanding, the general principles of these modes are as follows:

Power Delivery Mode (Active Power Transfer): During these intervals, diagonal pairs of primary switches (e.g., QA and QD, or QB and QC) are simultaneously turned ON. This action applies the full input voltage (Vin) across the transformer primary winding. Consequently, power is actively transferred from the primary to the secondary side, and the primary current typically rises, contributing to the charging of the output filter inductor.²
Freewheeling Mode (Zero Voltage Across Transformer Primary): In this mode, either the two upper switches (QA and QC) or the two lower switches (QB and QD) are turned ON. This configuration effectively short-circuits the transformer primary. As a result, zero voltage is applied across the primary winding, and no power is transferred to the secondary side. During this period, the output power is sustained by the energy previously stored in the output inductance. The primary current freewheels through the shorted path, maintaining its previous state and preventing it from decaying to zero, which is crucial for ZVS.²
Duty Cycle Loss Mode: These modes occur during the brief transition intervals between the power delivery and freewheeling phases. During these periods, the primary current, influenced by the input voltage and the transformer’s leakage inductance, is actively charging or discharging the parasitic capacitances of the switches. No power is delivered to the output during these brief moments. The finite slope of the primary current’s rising and falling edges, which is a direct consequence of the leakage inductance, causes this “duty cycle loss.” This means the effective duty cycle observed on the secondary side is inherently less than that on the primary side.⁸
ZVS Transition Modes: These are critical sub-intervals that occur within the dead-time, the period when both switches in a leg are intentionally turned OFF. As a switch turns OFF, the primary current is redirected. This current then charges and discharges the parasitic output capacitances (Coss) of the switches in that leg, utilizing the energy stored in the resonant (leakage) inductance. This resonant action ensures that the voltage across the switch falls to (or very near) zero before it is turned ON, thereby enabling lossless switching and significantly reducing turn-on losses.²

The phenomenon of “duty cycle loss” observed in PSFB converters, while appearing to be a limitation, is a direct consequence of the very mechanism—the utilization of leakage inductance and resonant transitions—that enables Zero Voltage Switching. This presents a fundamental trade-off in design: achieving soft switching, which is essential for high efficiency at elevated frequencies, inherently reduces the effective duration for power transfer. To compensate for this reduction and maintain output voltage regulation, a wider control range or a higher switching frequency may be necessary. Such compensation, however, can exacerbate other design challenges, including increased circulating currents, particularly under lighter load conditions. This means that the “loss” is not a defect but an intrinsic characteristic of the soft-switching approach, highlighting a design challenge that requires careful balancing of parameters to optimize overall performance.

Table 1: Summary of PSFB Converter Operating Modes

Mode Name	Active Primary Switches	Transformer Primary Voltage (V_PRI)	Primary Current (I_PRI) Behavior	Secondary Side Behavior
Power Delivery (Positive)	QA & QD	+Vin	Rising/Constant	Power transferred to load, output inductor charges
ZVS Transition (Right Leg)	QA, (QD turning OFF)	Resonating (Vin to 0V)	Resonating (charging/discharging Coss)	Output inductor supplies load, primary contribution decays
Freewheeling (Top Switches ON)	QA & QC	0V	Freewheeling (constant/decaying slowly)	Output inductor supplies load, transformer shorted
ZVS Transition (Left Leg)	QC, (QA turning OFF)	Resonating (0V to -Vin)	Resonating (charging/discharging Coss)	Output inductor supplies load, primary contribution changes
Power Delivery (Negative)	QB & QC	-Vin	Rising/Constant	Power transferred to load, output inductor charges
ZVS Transition (Left Leg)	QB, (QC turning OFF)	Resonating (-Vin to 0V)	Resonating (charging/discharging Coss)	Output inductor supplies load, primary contribution decays
Freewheeling (Bottom Switches ON)	QB & QD	0V	Freewheeling (constant/decaying slowly)	Output inductor supplies load, transformer shorted
ZVS Transition (Right Leg)	QD, (QB turning OFF)	Resonating (0V to Vin)	Resonating (charging/discharging Coss)	Output inductor supplies load, primary contribution changes

This table provides a concise, structured overview of the converter’s dynamic operation, which is inherently complex and involves multiple interleaved states. It clarifies the role of each primary switch and the transformer at different times, directly linking the phase-shift control to the power transfer and soft-switching mechanisms. For engineers, this is critical for understanding the timing, control logic, and current paths, aiding in design and troubleshooting.

III. Soft Switching: Zero Voltage Switching (ZVS) and Zero Current Switching (ZCS)

Mechanism of Zero Voltage Switching (ZVS) for Primary Switches

The primary advantage of the PSFB topology is its inherent ability to achieve Zero Voltage Switching (ZVS) for all four power electronic switches on the primary side, typically MOSFETs or IGBTs. This capability is paramount for high-frequency operation, as it significantly reduces turn-on switching losses, leading to a substantial increase in overall converter efficiency and a reduction in electromagnetic interference (EMI). This benefit is particularly pronounced for high-voltage (HV) devices, where hard-switching losses would otherwise be considerable.¹

The fundamental principle behind ZVS relies on exploiting the resonant interaction between the parasitic output capacitances (Coss) of the MOSFETs and the leakage inductance (Llkg) of the high-frequency transformer. In many designs, an external resonant inductor (Lr), often referred to as a “shim” inductor, is deliberately added in series with the transformer primary winding to augment this leakage inductance. During the dead-time—the brief interval when both switches in a leg are intentionally turned OFF—the energy stored in this resonant inductance is strategically utilized. This stored energy charges and discharges the parasitic capacitances of the MOSFETs, ensuring that the voltage across the switch is ideally zero before it is turned ON. This resonant action enables soft switching, minimizing energy dissipation during turn-on.¹ It is worth noting that a larger resonant inductance generally allows ZVS to be maintained over a wider load range, though this can lead to increased duty cycle loss and a slight reduction in overall efficiency.²

Precise control of the dead-time is critical for successful ZVS. This intentional delay provides the necessary time for the resonant current, driven by the stored inductive energy, to fully charge and discharge the switch capacitances. Advanced control strategies, such as adaptive dead-time control, dynamically adjust this interval based on varying load conditions. This optimization ensures that ZVS performance is maintained or closely approached across the entire load range, thereby minimizing switching losses under diverse operating scenarios.¹

The achievement of ZVS can vary between the two legs of the full bridge due to their different roles in the power transfer cycle:

Leading Leg (e.g., QA/QB or Q1/Q2): Switches in this leg typically initiate the power transfer interval. The primary current is usually at a higher magnitude, and the reflected load current actively assists the resonant transition. Consequently, achieving ZVS for the leading leg switches is generally easier and can often be maintained across the complete load range.¹
Lagging Leg (e.g., QC/QD or Q3/Q4): Switches in this leg mark the end of the power transfer interval. During their transitions, the primary current may decrease, cross zero, and even reverse direction. This dynamic results in lower available energy for the ZVS transition, making it challenging to achieve full ZVS, especially under light-load conditions. In such cases, these switches may operate with “Low Voltage Switching” (LVS), where they turn ON when the voltage across them is at a minimum, rather than strictly zero, to minimize losses.¹

The load-dependent characteristic of ZVS, particularly the difficulty in achieving Zero Voltage Switching for the lagging leg under light load conditions, represents a fundamental limitation of the conventional PSFB topology. This implies that while PSFB delivers substantial efficiency gains at mid to full loads, its performance can diminish at lighter loads. This degradation necessitates the implementation of advanced control strategies, such as adaptive dead-time control or burst mode operation, or the integration of auxiliary circuits, to sustain high efficiency across the entire operational spectrum. The energy required for ZVS, which charges and discharges the parasitic capacitances, is derived from the current flowing through the resonant inductance. At light loads, this primary current is lower, meaning less stored energy is available to complete the resonant transition within the allotted dead-time. This inherent limitation translates directly to increased switching losses and reduced efficiency in an operating range where many modern applications, such as server power supplies in idle mode, demand high efficiency. This continuous effort to expand the ZVS range highlights the ongoing drive to optimize PSFB performance for diverse application requirements.

Mechanism of Zero Current Switching (ZCS) for Secondary Rectifiers

For power conversion systems characterized by low output voltage and/or high output current ratings, implementing synchronous rectification (SR) using MOSFETs on the secondary side of PSFB converters is a common practice. This approach is preferred over traditional diode rectifiers because it effectively avoids the significant conduction losses associated with diodes, thereby achieving superior overall performance and efficiency.¹

Zero Current Switching (ZCS) for secondary side synchronous rectifiers is achieved when the MOSFET is turned ON or OFF precisely at the moment its current is zero. This technique is critical because it eliminates switching losses associated with current commutation, particularly the reverse recovery losses that plague diodes (or the body diodes of MOSFETs when they conduct in reverse).²⁶

In a common current doubler rectifier configuration, the operation involves complex current paths and commutation sequences. For instance, when a primary switch turns ON with ZVS, the transformer secondary voltage can momentarily become zero. During this brief period, both secondary rectifiers (SR1 and SR2) may conduct, and the output inductors discharge. Active power transfer resumes only when the primary current reverses direction and rises to the level of the reflected output inductor current, allowing for proper current commutation.⁸

Despite the advantages of SR, achieving ZCS for secondary rectifiers presents its own set of challenges, particularly at light loads. When the PSFB converter operates in Discontinuous Conduction Mode (DCM) under light load conditions, the output inductor current may flow through the body diode of the synchronous rectifier instead of its low-resistance channel. This undesirable conduction through the body diode leads to increased losses and degrades efficiency.¹² To mitigate this issue, advanced adaptive control schemes are proposed. These schemes precisely modulate the turn-on time of the synchronous rectifiers, ensuring that the SR MOSFETs are actively switched ON when the current is truly zero. This eliminates body-diode conduction losses and significantly improves light-load efficiency without requiring additional auxiliary circuits.¹²

While the PSFB topology is widely recognized for achieving Zero Voltage Switching on its primary side, the implementation of Zero Current Switching for synchronous rectifiers on the secondary side presents its own distinct set of challenges, particularly under light load conditions. This situation underscores that optimizing the overall efficiency of the converter demands a comprehensive approach, addressing soft-switching conditions on both the primary and secondary sides. Simply achieving ZVS on the primary side is not sufficient to ensure peak performance across the entire operational range. The necessity for precise control over secondary-side rectifiers, especially through adaptive control schemes, demonstrates the continuous engineering effort to maximize efficiency from every component within the power path. This pursuit acknowledges that the total system efficiency is ultimately constrained by the least efficient element in the conversion chain. The body diode conduction is a direct consequence of the current commutation characteristics and the precise timing of SR gate signals relative to the inductor current. If the SR is not turned on at the precise zero-current crossing, or if the current reverses prematurely, the body diode conducts. This means that achieving high efficiency across the full load range, especially at light loads, requires sophisticated control of the secondary-side rectifiers, not just the primary switches.

Table 2: Comparison of ZVS/ZCS Achievement Across Load Ranges

Component Type	Soft Switching Type	Full Load Performance	Mid Load Performance	Light Load Performance	Notes
Primary Leading Leg Switches	ZVS	Achieved	Achieved	Achieved	Generally easier to achieve ZVS across full load range.
Primary Lagging Leg Switches	ZVS/LVS	Achieved	Achieved	Lost/Difficult	Often operates with Low Voltage Switching (LVS) at light loads; requires adaptive control or auxiliary circuits.
Secondary Rectifiers (Diodes)	Hard Switching	Hard Switching	Hard Switching	Hard Switching	High conduction losses, especially at low output voltages.
Secondary Rectifiers (Synchronous MOSFETs)	ZCS	Achieved (with proper control)	Achieved (with proper control)	Lost/Difficult	Can experience body diode conduction at light loads in DCM; requires adaptive control to eliminate.

This table offers a clear, concise overview of the soft-switching performance for various components within the PSFB converter across its operational spectrum. It highlights the areas where the topology inherently excels and where it encounters limitations, such as the challenges in achieving ZVS for the lagging leg at light loads or managing body diode conduction in synchronous rectifiers under similar conditions. This information is invaluable for designers, as it helps identify critical operating points and determine where advanced control strategies or auxiliary circuits are essential to maintain high efficiency and reliability.

IV. Advantages of PSFB Converters

High Efficiency and Reduced Switching Losses

PSFB converters are widely recognized for their exceptional efficiency, typically achieving conversion efficiencies ranging from 90% to 95% at high operating frequencies. Certain optimized designs have demonstrated peak efficiencies exceeding 95%.¹ This high level of efficiency is primarily attributed to the implementation of Zero Voltage Switching (ZVS) for the primary side switches. ZVS nearly eliminates turn-on switching losses, which is particularly advantageous for high-voltage (HV) devices where hard-switching losses would otherwise be substantial and contribute significantly to overall power dissipation.⁵ Furthermore, high efficiency can be maintained even at relatively light loads, with some PSFB systems demonstrating efficiencies exceeding 90% down to 10% of their rated load.¹

Low Electromagnetic Interference (EMI)

The soft-switching nature of PSFB converters inherently contributes to lower electromagnetic interference (EMI) emissions. Because ZVS ensures that switches turn on when the voltage across them is zero, the rate of change of voltage (dv/dt) during switching transitions is significantly reduced compared to hard-switched PWM bridges. This smoother switching action minimizes the generation of high-frequency noise, leading to improved EMI performance.² Additionally, the constant switching frequency characteristic of PSFB converters simplifies the design and filtering requirements for EMI, as the noise spectrum is concentrated at predictable frequencies. This contrasts with variable-frequency topologies like LLC resonant converters, where EMI filtering can be more complex. Techniques such as dithering, which spreads EMI energy over a wider frequency band, are also easier to implement with fixed-frequency PSFB converters.⁹

High Power Density and Scalability

The ability of PSFB converters to operate at high switching frequencies, a direct benefit of their soft-switching capabilities, allows for the use of smaller magnetic components, including transformers and inductors. This reduction in component size directly translates to a significant decrease in the overall volume and weight of the converter, thereby achieving a higher power density.³ PSFB converters are also inherently scalable for high-power applications, capable of delivering twice the power compared to a half-bridge design. Their constant frequency operation further simplifies the paralleling of multiple modules for increased power output and facilitates easier current sharing among individual units, contributing to robust and scalable power solutions.²

Galvanic Isolation

A fundamental and non-negotiable characteristic of the PSFB topology is the inclusion of an isolation transformer. This component provides galvanic isolation between the input and output stages of the converter. Such isolation is a mandatory safety requirement in numerous applications, including telecommunications, medical equipment, and electric vehicle charging systems. Beyond safety, galvanic isolation is crucial for mitigating common-mode noise and preventing ground loops, thereby enhancing system reliability and performance.¹

Constant Switching Frequency Operation

Unlike resonant converters, such as the LLC topology, which regulate output voltage by varying their switching frequency, PSFB converters operate at a constant switching frequency. This characteristic offers several significant advantages. It simplifies the design of the control loop, as there is no need to track a resonant frequency. It also streamlines the design of EMI filters, as the noise spectrum is fixed. Furthermore, constant frequency operation greatly facilitates system-level features such as synchronization and current sharing when multiple PSFB units are paralleled, making multi-module systems more manageable and robust.⁹

Reduced Voltage Stress on Primary Switches

The design of a PSFB converter inherently limits the voltage stress on its primary side switches (MOSFETs or IGBTs) to the input voltage (Vin). This characteristic allows for the selection of lower voltage-rated components for the primary switches. Lower voltage-rated devices often exhibit better conduction characteristics, such as lower ON-resistance (Rds(on)), which directly contributes to higher overall efficiency by reducing conduction losses.²

Elimination of Primary Snubber Circuits

Due to its inherent Zero Voltage Switching (ZVS) capability, PSFB converters generally do not require additional dissipative snubber circuits on the primary side. Snubber circuits are traditionally used to reduce switching losses and voltage spikes in hard-switched converters. By eliminating the need for these components, the PSFB topology simplifies the overall circuit design, reduces component count, and further contributes to higher efficiency by avoiding the power dissipation associated with snubber networks.²

The combination of Zero Voltage Switching and constant frequency operation in PSFB converters creates a synergistic effect that streamlines the overall system design beyond just the power stage. This includes easier compliance with electromagnetic interference (EMI) standards, straightforward paralleling of multiple units, and potentially simpler control loop implementation compared to topologies with variable operating frequencies. This makes PSFB a more “system-friendly” choice for complex power systems. The underlying principle is that by controlling switching transitions to occur at zero voltage, the rate of change of voltage (dv/dt) is reduced, which inherently lowers high-frequency noise and simplifies EMI filtering. Simultaneously, maintaining a fixed switching frequency eliminates the challenges associated with frequency tracking, which can complicate control algorithms and lead to audible noise or synchronization issues in multi-module setups. This integrated benefit positions PSFB as a topology that not only offers high efficiency but also contributes to reduced complexity and cost at the system level, particularly in high-power, multi-module applications where precise coordination is essential.

V. Common Applications of PSFB Converters

Telecommunications Systems

PSFB converters are frequently deployed in telecommunications rectifiers, where they perform the critical function of stepping down high DC bus voltages, such as 400V, to intermediate distribution voltages, typically around 48V. In these applications, the galvanic isolation provided by the integrated transformer is not merely a feature but a critical safety and performance requirement. It ensures robust protection between the high line voltage and the sensitive downstream telecommunications equipment, preventing ground loops and enhancing system reliability.¹

Server Power Supplies

In the demanding environment of server power supplies, PSFB converters serve as the front-end DC-DC converter stage. They are responsible for converting regulated DC bus voltages, often around 390V from a Power Factor Correction (PFC) stage, to lower, tightly regulated outputs such as 12V, 24V, or 48V. High efficiency is of paramount importance in data centers, given the enormous power consumption of server racks. Industry standards, like the 80 PLUS certifications, increasingly mandate high efficiency even at light loads. The PSFB’s wide Zero Voltage Switching (ZVS) range from mid to full load makes it a strong candidate for meeting these stringent efficiency requirements.¹ Furthermore, the common use of redundant structures in server power supplies, where multiple parallel units share the total load, greatly benefits from the PSFB’s constant switching frequency operation, which simplifies current sharing and synchronization among modules.⁹

Electric Vehicle (EV) Charging Systems

PSFB converters are extensively employed in battery charging systems, encompassing both on-board and off-board electric vehicle (EV) chargers, as well as dedicated EV charging stations. This topology is well-suited for applications demanding a wide conversion range, a crucial feature for charging various battery chemistries, such as Lithium-ion and Lead-acid, which necessitate precise voltage regulation during different charging phases (ee.g., constant current, constant voltage, and top-up).¹ The inherent capability of PSFB converters for bidirectional power flow, when employing synchronous rectification on the secondary side, further extends their utility into advanced applications like vehicle-to-grid (V2G) systems, enabling energy transfer both to and from the vehicle.⁶

Renewable Energy Systems

PSFB converters are integral components within modern renewable energy infrastructures, including solar power generation systems and large-scale energy storage systems. They facilitate efficient DC-DC conversion and provide essential isolation in these high-power applications. Their robust performance contributes significantly to the overall efficiency and reliability of both grid-tied and off-grid renewable energy solutions, ensuring stable power delivery from intermittent sources.¹

Industrial Power Systems and Auxiliary Power Units (APUs)

Beyond the specific applications mentioned, PSFB converters serve as a versatile solution for high-power regulators and a wide array of industrial equipment. They are also found in Auxiliary Power Units (APUs) within electric vehicles, where they convert the high voltage from the battery pack to lower voltages required for internal loads such as electric power steering, electric turbochargers, and cooling pumps.² Their high power density and soft-switching capabilities make them particularly suitable for the demanding and often harsh environments characteristic of industrial settings.

The consistent demand for galvanic isolation across nearly all major PSFB applications—including telecommunications, server power supplies, electric vehicle charging, renewable energy systems, and various industrial power systems—highlights that isolation is not merely a supplementary feature but a fundamental requirement driving topology selection in these high-power, safety-critical, and noise-sensitive environments. This pervasive need for isolation elevates it to a primary design driver and a core competitive advantage for PSFB converters over non-isolated topologies. The presence of a transformer within the PSFB topology inherently provides this isolation, serving multiple crucial functions: it ensures safety by preventing dangerous voltages from reaching users or sensitive downstream equipment; it reduces noise by breaking ground loops and preventing common-mode noise propagation; and it aids in fault containment by limiting fault currents. Thus, the inherent isolation capability of PSFB converters is a key factor in their widespread adoption and continued relevance in these demanding sectors.

VI. Design Considerations and Challenges

Transformer Design

The high-frequency transformer is a central and indispensable component within the PSFB converter topology. It serves the dual critical roles of providing galvanic isolation and performing voltage translation, and its design profoundly impacts the converter’s overall performance, efficiency, and physical size.¹

Leakage Inductance (Lr/Llkg): This is a particularly critical parameter in PSFB transformer design. Unlike conventional transformers where it is minimized, leakage inductance is intentionally utilized as an integral part of the resonant tank circuit to facilitate Zero Voltage Switching (ZVS). A larger leakage inductance, or the addition of an external series inductor, can extend the ZVS range, especially under lighter load conditions. However, an excessive amount of leakage inductance can lead to increased duty cycle loss (reducing the effective power transfer duration), lower overall efficiency, and can resonate with secondary diode capacitances, causing high voltage spikes and oscillations on the secondary side. These issues often necessitate the inclusion of additional clamping circuits.²
Magnetizing Inductance (Lm): The magnetizing inductance also plays a significant role in achieving ZVS, particularly at light loads, by assisting the resonant transition. Maximizing Lm can help reduce circulating current losses, but its value must be carefully chosen to avoid limiting the ZVS range or causing other undesirable effects.¹⁶
Turns Ratio (N): The transformer’s turns ratio (Ns/Np) is selected to ensure full power delivery at the minimum specified input voltage. A lower turns ratio increases the primary current, which can extend the ZVS range at light loads. However, this also increases the reflected voltage stress on the secondary side rectifiers, requiring careful component selection.¹⁷
Core Material and Winding Techniques: High-frequency operation necessitates the careful selection of core materials to minimize core losses, which become more significant at higher frequencies. Winding techniques profoundly influence the parasitic elements. For instance, non-interleaved or two-chamber winding arrangements can be used to intentionally increase leakage inductance, while full interleaving can reduce it, often at the cost of higher interwinding capacitance. These choices directly impact the converter’s efficiency, EMI performance, and thermal management.¹⁷
Parasitic Capacitance (Cxfmr): The inherent transformer capacitance, along with the winding capacitance, can resonate with the leakage inductance. These parasitic capacitances can cause current spikes on the primary side and contribute to unwanted ringing on the secondary side, potentially increasing component stress and noise.¹⁸

The transformer in a PSFB converter is not merely a passive component for isolation and voltage transformation but an active participant in the soft-switching mechanism. This means its parasitic elements (leakage inductance, capacitance) are designed into the resonant tank rather than minimized, creating a complex multi-objective optimization problem where ZVS range, efficiency, voltage spikes, and physical size are interdependent. This approach means that the transformer’s physical construction, including its winding arrangements and core geometry, directly dictates the resonant properties that enable ZVS. This transforms transformer design from a simple turns ratio and power rating calculation into a sophisticated multi-variable optimization challenge. Designers must carefully balance the need for sufficient leakage inductance to ensure ZVS over a wide load range against the increased duty cycle loss, potential voltage spikes, and AC winding losses that larger leakage inductance can introduce. The transformer’s “imperfections” thus become critical design tools, making its design a highly specialized and intricate aspect of PSFB optimization, requiring deep understanding of its parasitic effects.

Selection of Switching Devices (MOSFETs, IGBTs, SiC, GaN)

The choice of power switches for both the primary and secondary sides is a pivotal decision that directly influences the converter’s efficiency and overall performance. PSFB converters typically employ either MOSFETs or IGBTs.¹

MOSFETs vs. IGBTs:
- MOSFETs: These devices are generally preferred for high-frequency applications (e.g., >100 kHz) and lower current densities due to their lower ON-resistance (Rds(on)) at lower voltages. Their inherent parasitic output capacitance (Coss) and body diode are essential elements that are actively utilized in the ZVS mechanism to achieve soft switching.¹⁵
- IGBTs: Insulated Gate Bipolar Transistors (IGBTs) offer advantages in high-current density and lower-frequency applications (typically <20 kHz) due due to their lower ON-state voltage drop and superior current density capabilities. However, the presence of a “tail current” during their turn-off process limits their performance at higher switching frequencies and can contribute to increased switching losses.⁵⁰
Wide-Bandgap Semiconductors (SiC and GaN):
- Advanced wide-bandgap (WBG) semiconductors, such as Silicon Carbide (SiC) and Gallium Nitride (GaN) FETs, are increasingly being adopted in PSFB designs. These materials enable designers to push the boundaries of efficiency and power density beyond what is achievable with traditional silicon devices. They offer substantial improvements, including significantly lower gate capacitance, which facilitates faster turn-on and turn-off times with reduced gate drive losses, and overall superior figures of merit (FOMs).²⁹
- GaN FETs: Gallium Nitride FETs are particularly advantageous for PSFB applications due to their exceptionally smaller output capacitances. This characteristic can extend the ZVS range to lighter loads even without the need for complex auxiliary circuits, simplifying the design. Additionally, GaN devices typically lack a body diode, which eliminates reverse-recovery losses, further boosting efficiency. GaN FETs are commonly rated for 600V and are well-suited for high-density converters operating at power levels of 10kW and higher.³⁰
- SiC FETs: Silicon Carbide FETs offer higher voltage capabilities, often up to 1200V, coupled with high current-carrying capabilities. This makes them ideal for very high-power applications, such as automotive traction inverters and large solar farms. While SiC FETs do possess a body diode and thus incur some reverse-recovery losses, their overall performance, particularly at high voltages and temperatures, is superior to traditional silicon devices.⁵¹

The continuous evolution of semiconductor technology, particularly the emergence of Silicon Carbide (SiC) and Gallium Nitride (GaN) devices, is fundamentally transforming the landscape of PSFB converter design. These advancements directly address some of the long-standing limitations of conventional silicon-based PSFB designs. For instance, the significantly smaller output capacitances of GaN FETs directly facilitate ZVS at lighter loads, a common challenge for PSFB converters. Furthermore, the faster switching speeds and reduced losses associated with both SiC and GaN enable higher operating frequencies, which in turn allows for the use of smaller passive components, leading to increased power density. The absence of a body diode in GaN devices also eliminates reverse-recovery losses, further boosting efficiency. This technological progression means that PSFB converters can achieve higher performance levels, particularly in terms of efficiency across a wider load range and increased power density, thereby expanding their applicability into new domains or enhancing their competitiveness in existing ones. This illustrates how innovation at the component level directly impacts the overall system capabilities and extends the operational envelope of the PSFB topology.

Control Strategies

Effective control is paramount for PSFB converters to achieve desired output regulation, maintain soft switching conditions, and optimize efficiency across varying load and input conditions.

Phase Shift Control: As the primary control mechanism, the phase shift between the two primary legs of the full bridge is continuously adjusted. This adjustment regulates the amount of energy transferred from the input to the output, thereby maintaining the output voltage at the commanded level. This method forms the core of PSFB’s power regulation capability.¹
Peak Current Mode Control (PCMC) and Voltage Mode Control (VMC): Both Peak Current Mode Control (PCMC) and Voltage Mode Control (VMC) schemes are implemented in PSFB systems. PCMC is highly favored due to its inherent advantages, which include automatic cycle-by-cycle current limiting, effective flux balancing in the transformer, and built-in voltage feed-forward. However, implementing PCMC for PSFB requires the generation of complex PWM waveforms with extremely precise timing control.¹
Digital Control: The ongoing transition to digital power control, often implemented with high-performance microcontrollers (MCUs) such as the C2000 series, has significantly enhanced the capabilities of PSFB converters. MCUs can effectively close control loops, generate complex PWM waveforms with intelligent timing control, and implement sophisticated advanced control strategies. This digital approach simplifies the overall system by shifting many functions traditionally performed by hardware into flexible software algorithms.¹
Adaptive Dead-Time Control: To address the load-dependent ZVS characteristic, adaptive dead-time control dynamically adjusts the dead-time for the primary side switches based on real-time operating conditions. This ensures that ZVS or at least Low Voltage Switching (LVS) is achieved across a wider load range, effectively minimizing switching losses under varying loads.¹
Burst Mode Control: For very light load conditions, burst mode control is employed to significantly improve efficiency. This technique involves periodically switching the output current between 0A and a minimum ZVS current. This effectively reduces the average switching frequency and the associated switching losses during idle or very light load operation.³⁷
Hybrid Control: Some advanced strategies combine different control methods to optimize efficiency across the entire load spectrum. For example, a hybrid approach might utilize conventional PWM control at very light loads to reduce circulating current loss, and then seamlessly switch to phase-shifted modulation for heavier loads to leverage the benefits of ZVS.⁴⁰
Model Predictive Control (MPC): Emerging as an advanced control strategy, Model Predictive Control (MPC) utilizes a theoretical model of the converter to calculate optimal control quantities. This approach has the potential to significantly improve dynamic performance. However, it demands high accuracy in system modeling and can be sensitive to parameter variations or external disturbances, requiring robust implementation.¹⁴

The proliferation of advanced digital control strategies, including adaptive dead-time, burst mode, hybrid control, and model predictive control, directly addresses the inherent trade-offs and limitations of conventional PSFB converters, particularly concerning light-load efficiency and the range over which Zero Voltage Switching can be maintained. This trend signifies a fundamental shift from purely hardware-centric power supply design to sophisticated, software-defined power management. The proliferation of powerful microcontrollers is a critical enabler for implementing these complex algorithms, allowing control logic to be flexible and adaptable rather than fixed. This implies that while the fundamental PSFB topology is robust, its full potential, especially for wide operating ranges and stringent efficiency standards (such as those required by 80 PLUS Titanium certifications ⁹), is unlocked through intelligent, software-driven control. This also suggests a higher barrier to entry for designers, who must now master these intricate control algorithms to achieve state-of-the-art performance.

Challenges

Despite its numerous advantages, the PSFB converter topology presents several inherent design challenges that must be meticulously addressed to ensure optimal performance across its operating range:

Circulating Current Loss: During the freewheeling intervals, a significant “circulating current” flows through the primary side switches and transformer windings. This current does not contribute to power transfer to the secondary side but instead increases conduction losses. This phenomenon is particularly pronounced at high input voltages and lighter loads, where it can significantly degrade overall efficiency.²
Loss of ZVS at Light Loads: As previously discussed, the energy required for Zero Voltage Switching (ZVS) is proportional to the square of the primary current. At light loads, this primary current decreases, making it difficult or even impossible to achieve ZVS for the lagging leg switches. This results in hard switching, which leads to increased switching losses and higher electromagnetic interference (EMI).²
Secondary Side Ringing and Voltage Spikes: The interaction between the transformer’s leakage inductance and the parasitic capacitances of the secondary rectifier diodes (or synchronous rectifiers) can cause severe voltage overshoot and high-frequency ringing across the rectifiers immediately after current commutation. This phenomenon increases voltage stress on the secondary components, potentially leading to device breakdown, and generates undesirable output voltage noise and EMI.¹⁷
Transformer Saturation: Subtle asymmetries within the PSFB converter’s operation can lead to a DC offset in the primary current waveform. This offset, if not properly managed, can cause a volt-second imbalance across the power transformer, potentially leading to core saturation and a runaway current condition, which can severely damage the transformer.²¹
Circuit Complexity: While simpler than some resonant topologies, the PSFB converter still involves dual high-side primary gate drives and necessitates precise timing control for its switching signals. These requirements contribute to the overall circuit complexity, particularly in terms of gate drive design and control implementation.²

Solutions and Advanced Techniques

Addressing the aforementioned challenges drives continuous innovation in PSFB converter design:

ZVS Extension Methods: Beyond adaptive dead-time control and burst mode operation, techniques to extend the ZVS range include optimizing the magnetizing inductance ¹⁶, adding external resonant inductors ¹⁶, and utilizing auxiliary LC branches or circuits. These auxiliary circuits are designed to provide additional energy for resonant transitions, particularly benefiting the lagging leg at light loads.¹⁶
Active Clamp Circuits: To mitigate secondary side ringing and voltage spikes, active clamp legs (typically consisting of a capacitor and a MOSFET) can be strategically inserted before the output inductor. These circuits effectively clamp the secondary winding voltage and rectifier stress, and unlike passive snubbers, they circulate the ringing energy losslessly. This approach significantly improves efficiency and can even achieve ZVS for the clamp MOSFET itself.⁴⁹
Hybrid PSFB Topologies: Integrating the PSFB with other converter topologies, such as LLC resonant converters or active current doubler rectifiers, can combine their respective advantages. For example, a hybrid PSFB-LLC converter can improve ZVS for lagging leg switches at light loads while retaining the PSFB’s high power capability and wide conversion range.⁵⁵
Transformer Saturation Prevention: Methods to prevent transformer saturation include the use of DC blocking capacitors in series with the transformer primary (though these can be bulky and introduce additional failure modes). Alternatively, Peak Current Mode Control (PCMC) with slope compensation can be employed, as it offers inherent flux balancing capabilities, effectively preventing saturation.¹

The continuous development of solutions for the inherent challenges of PSFB converters—such as circulating current, the loss of Zero Voltage Switching at light loads, secondary-side ringing, and transformer saturation—indicates that this is a mature yet actively evolving topology. This suggests that while PSFB offers strong baseline performance, achieving state-of-the-art efficiency and reliability across a wide operating range frequently necessitates the integration of these complex, multi-faceted solutions. Implementing these advanced techniques adds to the overall design effort and cost. The necessity of implementing these solutions, especially for demanding applications or wide operating ranges, means that a “simple” PSFB design might not meet all performance targets. Achieving peak performance requires integrating multiple, often complex, sub-systems. This increases design complexity, component count, and potentially overall cost. Therefore, the PSFB, while a robust foundational topology, achieves its high-performance realization through continuous engineering efforts to overcome its intrinsic limitations via sophisticated design and control. Consequently, it is best characterized as a highly optimized, rather than inherently simple, high-performance solution.

VII. Comparison with Other Isolated DC-DC Converter Topologies

PSFB vs. Hard-Switched Full-Bridge Converters

The fundamental distinction between PSFB converters and conventional hard-switched full-bridge converters lies in their freewheeling modes. In a hard-switched full-bridge, all four primary FETs are typically turned OFF during the freewheeling interval, leading to current decay. In stark contrast, the PSFB topology actively shorts the transformer primary by turning ON either both top FETs (QA and QC) or both bottom FETs (QB and QD) simultaneously. This deliberate short-circuit prevents the primary currents from decaying to zero, a crucial condition for enabling Zero Voltage Switching (ZVS).⁴

In terms of efficiency, PSFB converters offer a significant improvement by achieving ZVS for their primary switches, which drastically reduces switching losses, particularly at high input voltages (e.g., >200V). Hard-switched converters, conversely, incur substantial turn-on and turn-off losses due to the simultaneous overlap of voltage and current during switching transitions.⁴ Regarding EMI performance, ZVS in PSFB results in lower dv/dt rates during switching, leading to inherently better electromagnetic compatibility compared to the sharp, high-frequency transitions characteristic of hard-switched PWM bridges.¹¹ While PSFB converters require more complex PWM waveform generation and precise timing control compared to basic hard-switched PWM, the substantial benefits in efficiency and EMI performance often justify this added complexity for high-power applications.¹

PSFB vs. LLC Resonant Converters

Both PSFB and LLC resonant converters are prominent choices for high-power DC-DC conversion (typically >1 kW) and are capable of achieving Zero Voltage Switching (ZVS) for their primary switches.¹⁰ However, several key differences distinguish them:

ZCS Capability: LLC converters can additionally achieve Zero Current Switching (ZCS) in their rectifiers when operating at or below the resonant frequency. PSFB, on the other hand, typically does not inherently achieve ZCS for its secondary rectifiers without specialized control schemes.¹⁰
Operating Frequency and Control: A major differentiator lies in their frequency control. PSFB converters operate at a constant switching frequency, which simplifies control loop design, EMI filtering, system synchronization, and the paralleling of multiple modules. In contrast, LLC converters regulate their output voltage by varying their switching frequency around their resonant frequency. This variable frequency operation complicates synchronization and current sharing in multi-module systems, often necessitating complex digital control solutions.⁹
Efficiency Profile: While LLC converters can be highly efficient when operated near their resonant frequency, PSFB might exhibit higher RMS currents and greater power dissipation in its switches for a given Rds(on) compared to LLC. Nevertheless, PSFB converters consistently achieve high efficiencies, typically in the 90-95% range.²
EMI: PSFB’s fixed switching frequency simplifies EMI filter design, although its sharper current edges can lead to more high-frequency content. LLC converters generally produce less noise due to their resonant current waveforms.¹⁰
Design Complexity: LLC converter design can be an iterative process, and optimization can be challenging due to the intricate interplay of gain and frequency curves. PSFB is often considered easier to design and more “system-friendly” due to its fixed frequency operation.¹⁰
Component Requirements: LLC converters require a resonant capacitor for proper operation. PSFB converters, particularly when employing voltage mode control, may require a larger and potentially more expensive DC-blocking capacitor.¹⁰
Conversion Range: PSFB generally offers a wider conversion range and better output trim range and transient response, making it highly suitable for applications requiring a wide output voltage range, such as battery chargers. LLC’s voltage gain is a function of its switching frequency, which can limit its capability for very wide gain ranges.⁹

PSFB vs. Dual Active Bridge (DAB) Converters

Dual Active Bridge (DAB) converters are a prominent choice for isolated bidirectional DC-DC conversion, frequently employed in applications involving solar power, battery storage systems, and grid-tied inverters.³

Bidirectional Capability: While PSFB can be adapted for bidirectional operation through the use of synchronous rectification, DAB is inherently designed for it and is generally preferred for high-power bidirectional applications. PSFB in reverse mode can suffer from high conduction losses, increased switching losses due to reverse recovery, and large drain voltage overshoot in its switching devices.⁶
Soft Switching: Both PSFB and DAB topologies aim to achieve ZVS. However, conventional DAB converters can struggle with full-range soft switching at light loads or under mismatched gain conditions, similar to the ZVS challenges faced by the lagging leg of PSFB converters. Advanced DAB variants, such as DAB-SRC (Series Resonant Converter), can achieve improved soft-switching ranges.⁶⁰
Efficiency Profile: DAB converters can achieve higher efficiency at heavy loads due to lower conduction losses. In contrast, LLC (which can be considered a resonant DAB variant) might be more efficient at lighter loads due to its lower switching losses.⁶¹
Complexity: The basic DAB structure is relatively simple. However, achieving full-range soft-switching and optimal performance often involves increasing the degrees of freedom in control, leading to higher control complexity. For unidirectional power flow, PSFB is generally considered to have lower complexity than DAB.⁴³
Current Waveforms: Resonant DABs, such as DAB-SRC, typically produce almost sinusoidal current waveforms. This characteristic leads to smaller higher-order harmonics and consequently allows for reduced filter size. PSFB’s primary current, due to its sharper edges, tends to have more high-frequency content.¹⁰

The selection among PSFB, LLC, and DAB topologies represents a multi-dimensional optimization challenge, rather than a clear-cut choice of a single “best” solution. Each topology excels in specific performance metrics and is ideally suited for particular application niches. For instance, PSFB’s constant switching frequency simplifies control and EMI filtering, while LLC offers Zero Current Switching in its rectifiers. DAB, on the other hand, is inherently designed for bidirectional power flow. This means that the “ideal” solution is highly context-dependent, necessitating a deep understanding of the system-level trade-offs involved. Factors such as the required power level, input/output voltage range, need for bidirectionality, efficiency targets across the load spectrum, EMI constraints, and overall system complexity must all be carefully considered. The decision-making process requires a holistic evaluation of these interdependencies to select the topology that best aligns with the specific application’s demands.

VIII. Conclusion

The Phase-Shifted Full-Bridge (PSFB) converter stands as a highly effective and widely adopted topology for isolated DC-DC power conversion in medium to high-power applications. Its core strength lies in its ability to achieve Zero Voltage Switching (ZVS) for primary-side switches, significantly reducing switching losses and leading to high efficiencies, typically in the 90-95% range. This soft-switching capability also contributes to lower electromagnetic interference (EMI) and enables operation at higher switching frequencies, which in turn facilitates higher power density through smaller magnetic components. The inherent galvanic isolation provided by its transformer is a critical safety and performance requirement across numerous demanding applications, including telecommunications, server power supplies, electric vehicle charging systems, and renewable energy installations. Furthermore, its constant switching frequency simplifies control design, EMI filtering, and system-level integration aspects like synchronization and current sharing in multi-module systems.

Despite these significant advantages, PSFB converters present several design challenges. These include circulating current losses during freewheeling intervals, the difficulty of maintaining ZVS for the lagging leg at light loads, the potential for secondary-side ringing and voltage spikes, and the risk of transformer saturation due to current imbalances. However, continuous innovation in control strategies and circuit design has provided effective solutions. Advanced digital control techniques such as adaptive dead-time control, burst mode operation, and hybrid control schemes address light-load efficiency and ZVS range limitations. The adoption of wide-bandgap semiconductors like SiC and GaN FETs further enhances performance by reducing parasitic capacitances and switching losses, pushing the boundaries of efficiency and power density. Moreover, techniques like active clamp circuits mitigate secondary-side ringing, and robust control methods prevent transformer saturation.

The choice of PSFB over other isolated topologies like hard-switched full-bridges, LLC resonant converters, or Dual Active Bridge (DAB) converters is not absolute but depends on specific application requirements. PSFB offers superior efficiency and EMI performance compared to hard-switched designs due to ZVS. While LLC excels in ZCS for rectifiers and can be highly efficient near resonance, PSFB’s fixed frequency simplifies system-level integration. For bidirectional power flow, DAB is often the preferred choice, though PSFB can be adapted. Ultimately, the PSFB converter remains a robust and continuously evolving solution, capable of delivering high performance in demanding power conversion scenarios through careful design, advanced control, and leveraging cutting-edge semiconductor technologies. Its enduring relevance is a testament to its fundamental strengths and the ongoing engineering efforts to optimize its performance across diverse operating conditions.